Time Synchronization for Cooperative Communication in Wireless Sensor Networks

Time synchronization is crucial for the implementation of cooperative communication in wireless sensor networks. In this paper, we explore the effect of synchronization error on cooperative communication utilizing distributed Alamouti code. The analysis and simulation results show that small synchronization error has negligible effect on bit error rate (BER) performance. In order to synchronize the distributed sensor nodes within an acceptable error, we propose a physical layer synchronization scheme. This scheme consists of an initial synchronization of the cooperative transmitters, synchronization error estimation at the cooperative receiver and finally a feedback phase. A maximum likelihood method is proposed to make the synchronization error estimation. It achieves better performance than the matched filter method at the price of moderate increase in computational complexity and memory space. Two strategies after synchronization error estimation have been analyzed. They provide better BER performance in the existence of initial synchronization error. They are practical to be implemented in the sensor nodes before the Alamouti decoding.     

一种无线传感器网络自适应协同通信路由协议

无线传感器网络的重要应用特性是具有感测信息的传感节点形成一个自适应本地网络,由中心节点执行不同的协作信息处理任务。该文基于互信息量分析了不同中心节点选择机制的开销性能,证明了基于扩散计算的选择机制的开销有效性;提出一种自适应协同通信路由协议(ACCRP)：节点以分布式的方式选择中心节点并建立传输路径;分析讨论了ACCRP的性能参数;并通过实验验证了ACCRP是能源有效的、可扩展的自适应路由协议。     

MRL-SCSO: Multi-agent Reinforcement Learning-Based Self-Configuration and Self-Optimization Protocol for Unattended Wireless Sensor Networks

Resource-constrained nodes in unattended wireless sensor network (UWSN) operate in a hostile environment with less human intervention. Achieving the optimal quality of service (QoS) in terms of packet delivery ratio, delay, energy, and throughput is crucial. In this paper, we propose a topology control and data dissemination protocol that uses multi-agent reinforcement learning (MRL) and energy-aware convex-hull algorithm, for effective self-configuration and self-optimization (SCSO) in UWSN, called MRL-SCSO. MRL-SCSO maintains a reliable topology in which the effective active neighbor nodes are selected using MRL. The network boundary is determined using convex-hull algorithm to maintain the connectivity and coverage of the network. The boundary nodes transmit data under high traffic load conditions. The performance of MRL-SCSO is evaluated for various nodes count and under different load conditions by using the Contiki’s Cooja simulator. The results showed that MRL-SCSO stabilizes the performance and improves QoS.     

Cooperative Caching in Wireless Multimedia Sensor Networks

The recent advances in miniaturization and the creation of low-power circuits, combined with small-sized batteries have made the development of wireless sensor networks a working reality. Lately, the production of cheap complementary metal-oxide semiconductor cameras and microphones, which are able to capture rich multimedia content, gave birth to what is called Wireless Multimedia Sensor Networks (WMSNs). WMSNs will boost the capabilities of current wireless sensor networks, and will fuel several novel applications, like multimedia surveillance sensor networks. WMSNs introduce several new research challenges, mainly related to mechanisms to deliver application-level Quality-of-Service (e.g., latency minimization). To address this goal in an environment with extreme resource constraints, with variable channel capacity and with requirements for multimedia in-network processing, the caching of multimedia data, exploiting the cooperation among sensor nodes is vital. This article presents a cooperative caching solution particularly suitable for WMSNs. The proposed caching solution exploits sensor nodes which reside in “positions” of the network that allow them to forward packets or communicate decisions within short latency. These so-called “mediator” nodes are selected dynamically, so as to avoid the creation of hot-spots in the communication and the depletion of their energy. The mediators are not more powerful than the rest of the nodes, but they have some special role in implementing the cooperation among the sensors. The proposed cooperative caching protocol includes components for locating cached data as well as for implementing data purging out of the sensor caches. The proposed solution is evaluated extensively in an advanced simulation environment, and it is compared to the state-of-the-art cooperative caching algorithm for mobile ad hoc networks. The results confirm that the proposed caching mechanism prevails over its competitor.     

Communication Coverage in Wireless Passive Sensor Networks

System lifetime of wireless sensor networks (WSN) is inversely proportional to the energy consumed by critically energy-constrained sensor nodes during RF transmission. In that regard, modulated backscattering (MB) is a promising design choice, in which sensor nodes send their data just by switching their antenna impedance and reflecting the incident signal coming from an RF source. Hence, wireless passive sensor networks (WPSN) designed to operate using MB do not have the lifetime constraints of conventional WSN. However, the communication performance of WPSN is directly related to the RF coverage provided over the field the passive sensor nodes are deployed. In this letter, RF communication coverage in WPSN is analytically investigated. The required number of RF sources to obtain interference-free communication connectivity with the WPSN nodes is determined and analyzed in terms of output power and the transmission frequency of RF sources, network size, RF source and WPSN node characteristics.     

基于准格型策略的无线传感网协作覆盖算法

该文提出了一种基于准格型策略的无线传感网协作覆盖QGCC(Quasi-Grid based Cooperative Coverage)算法,通过在随机分布节点中构造准格型结构并结合协作感测模型,减少活动节点数量,延长覆盖周期。QGCC设计了低复杂度的分布式虚拟网格确定方法及能量高效的节点调度策略,定义了不规则度指标以分析网络的不规则程度对覆盖性能的影响。仿真实验表明,相比于参照算法,QGCC能够较大程度地减少活动节点的数量,大幅延长网络的覆盖周期;此外,该算法的覆盖周期和节点密度具有近似线性的关系,且比参考算法具有更大的斜率,说明其对冗余节点具有更高的利用效率。     

Cooperative Space-Time Block Codes for Wireless Video Sensor Networks

Wireless video sensor networks (WVSNs) are gaining popularity due to numerous potential applications such as video surveillance, environmental and habitat monitoring, and so on. Considering large-scale WVSNs, in which the sink node is not within the range of all other nodes, a multi-hop operation is desired. This paper proposes a novel cooperative system that uses space time-block codes to enhance the performance of multi-hop wireless video sensor networks. The proposed scheme is designed to deal with large-scale WVSNs, by adapting the cluster size and extending the cooperation between the cluster-heads. The performance comparison between the proposed system and a non-cooperative scheme is presented based on network lifetime for varying propagation scenarios, number of camera nodes, and on the quality of transmitted videos in a WVSN. Simulation results show an improvement in performance for the proposed system.     

Coping with Network Dynamics Using Reinforcement Learning Based Network Optimization in Wireless Sensor Networks

Due to the constant increase of in density of wireless network devices, inter-network cooperation is increasingly important. To avoid conflicts, advanced algorithms for inter-network optimization utilize cognition processes such as reinforcement learning to enable networks to become capable of solving complex optimization problems on their own with minimal outside intervention. This paper investigates the inherent trade-offs that occur when using reinforcement learning techniques in dynamic networks: the need to keep the network running optimally whilst, at the same time, different (suboptimal) network settings need to be continuously investigated to cope with changing network conditions. To cope with these network dynamics, two existing algorithms, “epsilon greedy” and Softmax, are compared to a novel approach, based on a logarithmic probability distribution function. It is shown that, depending on the expected level of dynamics, the new algorithm outperforms existing solutions.     

Cooperative Distributed MIMO Channels in Wireless Sensor Networks

The large number of network nodes and the energy constraints make Wireless Sensor Networks (WSN) one of the most important application fields for Cooperative Diversity. Node cooperation increases the spatial diversity of wireless channels and, thus, reduces the transmitted power. In this paper, we propose a multi-hop WSN with nodes grouped in cooperative clusters that exploits transmit and receive cooperation among cluster nodes. Multi-hop transmission is carried out by concatenating single cluster-to-cluster hops, where every cluster-to-cluster link is defined as a cooperative distributed multiple-input-multiple-output (MIMO) channel. Transmit diversity is exploited through a time-division, decoder-and-forward, relaying scheme based upon two time slots: the Intracluster Slot, used for data sharing within the cluster, and the Intercluster Slot, used for transmission between clusters. At the receiver side, a distributed reception protocol is devised based upon a Selection Diversity algorithm. The proposed multi-hop cooperative WSN is optimally designed for minimum end-to-end outage probability by deriving the optimum time and power allocated on the intracluster and intercluster slots of every single hop, given a per-link energy constraint. A simplified suboptimum resource allocation is also proposed, which performs close to the optimal policy. Results show that the proposed scheme achieves diversity equal to the equivalent MIMO system and significantly reduces energy consumption with respect to. the non-cooperative channel     

协同通信在无线传感网中的应用

差错性能、吞吐量一直是无线通信追求的关键参数,协同通信可以在终端不安装多天线的基础上获得近似MI-MO(Multiple Input Multiple Output)技术的协同分集增益,提高系统性能或吞吐量。能效性是无线传感网中的关键参数,将协同通信应用在基于分簇的无线传感器网络(WSN)中,可以提高整个网络的能效性,以达到节省能量、延长整个网络寿命的目标。介绍了协同通信在无线传感器网络的结合应用方案,对这种结合的能效性能的最新研究给出了分析介绍,最后总结了研究的关键问题以及未来的发展趋势和研究方向。     

Reliable and Secure Cooperative Communication for Wireless Sensor Networks Making Use of Cooperative Jamming with Physical Layer Security

Interference is generally considered as the redundant and unwanted occurrence in wireless communication. This research work proposes a novel cooperative jamming mechanism for scalable networks like wireless sensor networks which makes use of friendly interference to confuse the eavesdropper and increase its uncertainty about the source message. The communication link is built with the help of Information theoretic source and channel coding mechanisms. The whole idea is to make use of normally inactive relay nodes in the selective Decode and Forward cooperative communication and let them work as cooperative jamming sources to increase the equivocation of the eavesdropper. In this work, eavesdropper’s equivocation is compared with the main channel in terms of mutual information and secrecy capacity.     

基于聚类的无线传感网络的合作MIMO传输方案

Wireless sensor network is becoming more and more popular in recent years, but energy-constrained characteristic of sensor nodes is one of the critical issues that we must consider in system design. In this paper, a cluster-based virtual V-BLAST transmission scheme is proposed to achieve energy savings for energy-constrained wireless sensor networks. In the proposed scheme, instead of using cluster member as cooperative nodes, multiple cluster heads cooperate to form virtual antenna array so that V-BLAST based virtual MIMO transmission can be implemented. Based on the communication energy consumption model, a way to optimize the parameters for the scheme is given. In addition, detailed simulation is performed to evaluate the performance of the proposed scheme for both densely and sparsely deployed sensor networks. Theoretical analysis and simulation results verify the energy efficiency of the proposed scheme.     

无线移动网络的协作通信方案研究

结合具体的无线Ad hoc网络,提出了机会性的根据网络实时状况选择最佳中继的协作MAC协议,并在NS-2仿真平台上实现,仿真结果表明,较常规的802.11 DCF协议,协作MAC方案有效地提高了网络的递交率。此外对采用RCPC编码协作的MAC协议进行了数值仿真。这些协议和方案可以直接或修改后应用于现有的Ad hoc等无线网络,在一定程度上可以实现跨层的机会协作通信和组网方案。     

A Contract-Based Model for Multiuser Cooperative Relay in Wireless Communication Networks

Cooperative communication utilizes multi-user spatial diversity to improve spectrum efficiency and channel capacity. However, due to the limited wireless network resource, the selfish relay nodes may be unwilling to offer their relay assistance without any extra incentive. In this paper, the incentive issue between multiple wireless nodes’ relay service and multiple sources’ relay selection is investigated. By modelling multi-user cooperative relay as a labour market, a contract model is proposed with the combination of relay power and basic wage. A relay factor is introduced to describe the contract-relay strategy in cooperative communication. To incentivize the relay nodes to participate in multiple sources’ relay efficiently and credibly, an optimization problem of multi-user relay incentive is formulated to obtain the sources’ maximum cooperative utility under the individually rational restraints. By exploiting the hidden convexity of the non-convex problems in both single-source and multi-source scenarios, the efficient iterative algorithms are developed. Numerical results show that the performance of our approach yields a significant enhancement compared with the equal relay-power and equal relay-factor strategies.     

Reinforcement Learning for Multiple Access Control in Wireless Sensor Networks: Review, Model, and Open Issues

Wireless sensor networking is a viable communication technology among low-cost and energy-limited sensor nodes deployed in an environment. Due to high operational features, the application area of this technology is extended significantly but with some energy related challenges. One main cause of the nodes energy wasting in these networks is idle listening characterized with no communication activity. This drawback can be mitigated by the means of energy-efficient multiple access control schemes so as to minimize idle listening. In this paper, we discuss the applicability of distributed learning algorithms namely reinforcement learning towards multiple access control (MAC) in wireless sensor networks. We perform a comparative review of relevant work in the literature and then present a cooperative multi agent reinforcement learning framework for MAC design in wireless sensor networks. Accordingly, the paper concludes with some major challenges and open issues of distributed MAC design using reinforcement learning.     

无线传感器网络中协作通信的能耗优化方法研究

针对能量受限的无线传感器网络,该文综合考虑了协作节点数量和调制方式对系统能量有效性的影响,提出一种能量最优的综合优化方法。文中首先给出了在Rayleigh衰落信道环境下,协作通信系统采用二相相移键控(BPSK)和M进制正交幅度调制(MQAM)时误码率的闭式表达,同时对协作通信的系统能耗进行了分析。在此基础上,根据能耗最小化原则对协作节点数量和调制方式进行了联合优化。仿真结果表明,与调制方式固定或协作节点数固定的系统相比,该方案能进一步降低协作通信的系统能耗。     

能量有效的无线传感器网络协作压缩感知机制

单一的稀疏基无法适应无线传感器网络节点压缩感知过程的复杂性,该文提出一种适用于无线传感器网络的协作压缩感知策略,根据各自的能量消耗状态,节点之间以协作的方式选择稀疏基,进而,通过冗余字典增大数据表示过程中的稀疏度,并有效地增强传输过程的鲁棒性,达到降低能耗的目的。仿真结果表明该文提出的策略能够有效地延长网络生存时间,同时,数据恢复的准确性得到了极大地改善。     

城市移动无线传感器网络协同定位算法

随着无线传感器网络研究和应用的发展,城市规模的无线传感器网络开始出现,然而,其大规模、低成本、移动性和节点稀疏性等特性都给定位带来了困难.基于城市移动无线传感器网络的一种典型应用,研究了不依赖全球定位系统的无线传感器网络的定位问题,在曼哈顿环概率移动模型的基础上设计定位算法,并从理论和仿真两方面分析了该算法的收敛性和稳定性.